Commercial vehicles with a large number of gear positions frequently possess an auxiliary range gear train, which acts on the main drive shaft and engages itself with the existing gear stages. With such an auxiliary range gear train, it is possible that the total ratio of the main transmission is increased, since all gear stages of this main transmission can be employed along with each gear stage of the auxiliary range gear train, and in at least one gear stage of the auxiliary range gear train, the ratio of the gear stages of the main transmission are adjusted to be either under or over their designed ratio.
An auxiliary range gear train for automobiles has been made known by DE 41 21 709 A1. With a planet gear arrangement of this kind installed following the main transmission, the possibility exists, of operating the motor vehicle within the framework of the gear stages of its main transmission, respectively, in two different speed ranges. When shifted into a first, slow ratio stage of the auxiliary range gear train, the internal gear of the planetary transmission is coupled by means of a clutch to the transmission housing so that the output shaft of the auxiliary range gear train possesses a lesser speed of rotation than does the output shaft of the main transmission. In a second shifting stage, a direct through-drive from the output shaft of the main transmission onto the output shaft of the auxiliary range transmission is effected, whereby a clutch establishes a direct connection between the output shaft of the main transmission and the output shaft of the auxiliary range gear train. The shifting mechanism to carry this out is expensive in its design and fabrication.
As a further development, DE 198 51 895 A1 teaches an auxiliary range gear train constructed as a planet gear system. In this case, the internal gear of the planet gearing is non-rotatably bound to the housing of the transmission. The sun gear of the planetary transmission is coaxially aligned to the output shaft of the main transmission and, compared to the output shaft of the main transmission, it is free in its rotation. For the construction of a step-down ratio between the output shaft of the main transmission and the output shaft of the auxiliary range gear train, the sun gear can be non-rotatably bound with the output shaft of the main transmission. Once again, this design is complex, expensive in design and time consuming. Furthermore, the individual components raise problems with regard to support.
Thus the invention has the purpose of improving a planetary transmission and especially improving the component structure of the bearing support.